Overview – Rainbow Electronics DS28EA00 User Manual

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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO

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OVERVIEW

The block diagram in Figure 1 shows the relationships between the major function blocks of the DS28EA00. The
device has three main data components: 1) 64-bit Registration Number, 2) 64-bit scratchpad, and 3) alarm and
configuration registers. The 1-Wire ROM Function control unit processes the ROM function commands that allow
the device to function in a networked environment. The device function control unit implements the device-specific
control functions, such as read/write, temperature conversion, setting the chain state for sequence detection, and
PIO access. The CRC generator assists the master verifying data integrity when reading temperatures and
memory data. In the sequence detect process, PIOB functions as an input, while PIOA provides the connection to
the next device. The power supply sensor allows the master to remotely read whether the DS28EA00 has local
power available.

Figure 2 shows the hierarchical structure of the 1-Wire protocol. The bus master must first provide one of the eight
ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Conditional (“Alarm”) Search ROM,
5) Conditional Read ROM, 6) Skip ROM, 7) Overdrive-Skip ROM or 8) Overdrive-Match ROM. Upon completion of
an Overdrive ROM command byte executed at standard speed, the device enters Overdrive mode, where all
subsequent communication occurs at a higher speed. The protocol required for these ROM function commands is
described in Figure 12. After a ROM function command is successfully executed, the device-specific control
functions become accessible and the master may provide any one of the nine available commands. The protocol
for these control function commands is described in Figure 10. All data is read and written least significant bit
first.

Figure 1. DS28EA00 Block Diagram

Power Supply

Sensor

Internal V

64-Bit

Registration #

1-Wire ROM

Function Control

Device Function

Control

8-Bit CRC
Generator

Alarm and Config

Registers

64-Bit Scratchpad

Temperature

Sensor

PIOA

PIOB

(EN\)

(DONE\)

(ON\)